Valves in some internal combustion engines may be actuated by a camshaft having a plurality of rotating cams. The valves may be intake valves and/or exhaust valves coupled to cylinders in the engine. Tappets may be positioned between the cams and the valve stems to facilitate the transfer of energy from the camshaft to the valves, enabling actuation of the valves to perform combustion.
For example, U.S. Pat. No. 4,430,970 discloses a thermoplastic tappet positioned between a cam and a valve stem in order to reduce weight as compared to a metal tappet. However, the Inventors have recognized several drawbacks with using a thermoplastic tappet. For example, such tappets may have less compressive strength than metal tappets. As a result, the longevity of tappet may be decreased. Moreover, the thermoplastic tappet may become degraded when exposed to elevated temperatures during engine operation. Specifically, the thermoplastic tappet may deform due to elevated temperatures.
To address at least some of the aforementioned issues, a valve assembly is provided. The valve assembly may include a valve stem coupled to a spring and an impact dampening tappet partially enclosing the spring and the valve stem and in contact with a cam, the impact dampening tappet including an exterior metal layer having a cam contacting surface and an interior elastomeric layer traversing at least a portion of the interior surface of the exterior metal layer. The elastomeric layer enables the impact from the cam to the valve assembly to be reduced. This dampening reduces upstream as well as downstream force propagation caused by the impact between the cam and the tappet. As a result, the longevity of the valve, cam, and tappet is increased. Moreover, the likelihood of failure of the valve and the cam is decreased.
In some examples, the impact dampening tappet may further include an interior metal layer, the interior elastomeric layer being positioned between the exterior metal layer and the interior metal layer. Sandwiching the elastomeric layer between two metal layers holds the elastomeric layer in position, which reduces deformation of the elastomeric layer caused by temperature variations. Moreover, the sandwich construction provides improved spring-mass isolation, enabling damping of un-wanted frequencies, such as high frequencies.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.
FIGS. 2-5 and 7 are drawn approximately to scale, although other relative dimensions may be used, if desired.